@user495470's answer is correct for the question posed. The problem is neither
shred really make sense for modern systems.
This is mostly due to SSDs. Unlike magnetic disks, modern TRIM-enabled disks automatically clear deleted data in the background.
SSD's also perform wear leveling. This makes attempts to "over-write" a file both futile (you'll be writting to a different physical location) and undesirable (it needlessly contributes to disk wear).
All Macs that come with an SSDs have TRIM enabled.
The other problem the file system, specifically journaled file systems, which can keep a copy of data elsewhere before it's written out.
Even on magnetic media this can cause problems for both
All users [..] should be aware that srm will only work on file systems that overwrite blocks in place. In particular, it will NOT work on [..] the vast majority of journaled file systems.
[..] shred relies on a very important assumption: that the file system overwrites data in place. [..] many modern file system designs do not satisfy this assumption. Exceptions include: Log-structured or journaled file systems [..]
HFS Plus volumes are journaled by default since Mac OS X v10.3.
These days, the best way to securely "deleted" files is to enable FileVault (so they're never write disk unencrypted in the first place) then just delete them and let TRIM sort it out.
If, by stroke of misfortune, you're on a magnetic medium, have journalling disabled and, for some reason, can't encrypt the disk, you're options are:
rm -P which overwrites files with
0x00, and then
brew install coreutils && gshred secrets.txt)
srm has been removed from
homebrew-core but someone's published a tap here that works (ie.
brew install khell/homebrew-srm/srm && srm secrets.txt)
- Physical destruction of the medium :)